The present invention relates to an apparatus for performing a controlled operation on a workpiece and is concerned more particularly with an apparatus having changeable operating characteristics and the means and method by which the operating characteristics are changed.
In prior art plotting apparatuses such as disclosed in U.S. Pat. No. 3,330,182, issued to Gerber et al and having the same assignee as the present application, an optical light head is moved relative to a sheet of light sensitive material and selectively exposes the material in order to produce a plot of graphic information. The selective exposure occurs by projecting a beam of light from the head onto the sheet material to produce a light spot and then moving the sheet material and head relative to one another to move the spot along a predetermined path and expose the sheet material correspondingly. The exposure, when photographically developed, produces a line trace corresponding to the path traversed by the light spot and having a width corresponding to the width of the spot. Line traces can also be produced by flashing the light spot at consecutive positions on the sheet material. Additionally, individual flashes at selected locations on the sheet material expose the light sensitive material in accordance with the shape of the light spot.
In U.S. Pat. No. 3,330,182, referenced above, an aperture plate is provided in the light head with a plurality of individual apertures of different sizes and shapes. The apertures are situated in a circular array and by rotating the plate, individual apertures are brought into registration with the light beam projected onto the light sensitive material. By suitable optical means, the image of the aperture is focused on the materials so that the size and shape of the aperture controls the graphic image produced.
The mechanism which rotates the aperture plate in the referenced patent includes a drive motor engaged by means of suitable gearing with the circular periphery of the aperture plate and an encoder producing feedback signals in response to plate movement. The motor is controlled by an associated device such as the computer which operates the plotter, and the command signals generated by the computer are compared with feedback signals from the encoder in a closed loop system. Since the aperture plate is mounted in the light head for cooperation with the light beam, the drive motor and controls for the aperture plate are also mounted in the head. The motor and controls add to the overall weight and size of the head which increases the head inertia and correspondingly decreases the plotter performance and accuracy. With digitally controlled plotters in particular, it is desirable to have a plotting head which is as light as possible in order to handle a large volume of plotting data rapidly and maximize the plotter throughput.
It is, therefore, a general object of the present invention to provide a controlled apparatus with an improved means for changing the operating characteristics of a tool head. It is a further object of the present invention to provide a plotter having an adjustable plotting instrument in the head and mechanism separated from and engageable with the head for adjusting the instrument.